Water Supply in Times of Climate Change — Tracer Tests to Identify

Water supply in times of climate change — Tracer tests to identify the catchment area of an Alpine karst spring, Tyrol, Austria Schäffer, Rafael; Sass, Ingo; Heldmann, Claus-Dieter (2020)

DOI (TUprints): https://doi.org/10.25534/tuprints-00013341

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Water supply in times of climate change—Tracer tests to identify the catchment area of an Alpine karst spring, Tyrol, Austria

Rafael Schäffer, Ingo Sass & Claus-Dieter Heldmann

To cite this article: Rafael Schäffer, Ingo Sass & Claus-Dieter Heldmann (2020) Water supply in times of climate change—Tracer tests to identify the catchment area of an Alpine karst spring, Tyrol, Austria, Arctic, Antarctic, and Alpine Research, 52:1, 70-86, DOI: 10.1080/15230430.2020.1723853 To link to this article: https://doi.org/10.1080/15230430.2020.1723853

Published online: 11 Mar 2020.

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Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=uaar20 ARCTIC, ANTARCTIC, AND ALPINE RESEARCH 2020, VOL. 52, NO. 1, 70–86 https://doi.org/10.1080/15230430.2020.1723853

Water supply in times of climate change—Tracer tests to identify the catchment area of an Alpine karst spring, Tyrol, Austria Rafael Schäffer a, Ingo Sassa,b, and Claus-Dieter Heldmanna aInstitute of Applied Geosciences, Geothermal Science and Technology, Technische Universität Darmstadt, Darmstadt, Germany; bDarmstadt Graduate School of Excellence Energy Science and Engineering, Technische Universität Darmstadt, Darmstadt, Germany

ABSTRACT ARTICLE HISTORY Climate change and glacial retreat are changing the runoff behavior of Alpine springs and Received 20 June 2019 streams. For example, in the extremely dry and hot summer of 2018, many springs used for Revised 18 December 2019 drinking water supply lost up to 50 percent of their average discharge; a few springs have even Accepted 23 December 2019 run dry. In order to ensure drinking water supply in the future, springs featuring large and KEYWORDS constantly sufficient discharge rates will have to be identified and tapped. A case study was Uranine; karst; discharge/ undertaken at the Tuxbachquelle because catchment area and temporal variation of physico- runoff; rock glaciers; chemical and hydrochemical properties were previously unknown. Tracer tests with uranine Hochstegen Formation proved a hydraulic connection between this karst spring and a stream a few kilometers uphill. At low runoff, uranine needed about 4½ hours from the sink to the spring, whereas at high runoff more than four days was required. It became evident that discharge, electrical conductivity, temperature, and turbidity of the Tuxbachquelle respond within a few hours to precipitation events. The water quality and an examination of the water balance resulted in a significantly larger catchment area. It is assumed that widely karstified calcite marble subterraneously drains a considerable part of the Tuxertal (Tux Valley), including some active rock glaciers.

Introduction dominantly situated (Lambrecht and Kuhn 2007). With respect to the catchment areas of big Alpine rivers, such Motivation as the Rhône, Rhine, or Inn, the contribution of glacier melt The importance of glaciers and rock glaciers as water reser- reaches up to 25 percent of the total summer runoff (Huss voirs and for hydropower generation should be reevaluated 2011). Small catchment areas of several square kilometers for the future. Between 1850 and 2011, glaciers in the can derive their runoff almost completely from meltwater. Zillertal Alps lost about two thirds of their area (Fischer Permafrost and dead ice melt may add significant propor- et al. 2015). Within the Tuxertal (Tux Valley), the glacier tions and influence water composition (Winkler et al. 2016; area reduced from 20.6 km2 to 7.1 km2 between 1850 and Colombo et al. 2018; Brighenti et al. 2019). 2004 (Pröbstl and Damm 2009). Based on the latest Almost all active rock glaciers in eastern North Tyrol Tyrolean Geographic Information System (tiris) orthopho- are located in the Tuxertal. The area of these active rock tos of 2016 (Tyrolean Geographic Information System glaciers in the Tux Alps is estimated at 2.2 km2.The 2019), the glacier area totals only 5.2 km2.Thelossofglacial surface of another 230 inactive or fossil rock glaciers area and volume depends on several factors. Though no amounts to 9.1 km2 (Krainer and Ribis 2012). Active losses or slight glacier advances were observed in the 1970s rock glaciers can feature daily varying influences on dis- and 1980s, there has since been a significantly accelerating charge rates, chemical compositions including heavy glacier retreat (Gross 1987; Schwendiger and Pindur 2013; metal concentrations, and physical properties of down- Fischer et al. 2015). Minor glaciers smaller than 2 km2 are stream streams and springs (Krainer and Mostler 2002; much more affected by the decline than larger glaciers Thies et al. 2013; Nickus, Thies, and Krainer 2015). (Schwendiger and Pindur 2013).Icelossoccursmainlyat The Alps are more strongly affected by climate altitudes lower than 3,200 m. a.s.l., where small glaciers are change than other regions (Auer et al. 2007; Brunetti

CONTACT Rafael Schäffer [email protected] Institute of Applied Geosciences, Geothermal Science and Technology, Technische Universität Darmstadt, Schnittspahnstrasse 9, Darmstadt 64287, Germany. © 2020 The Author(s). Published with license by Taylor & Francis Group, LLC. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ARCTIC, ANTARCTIC, AND ALPINE RESEARCH 71 et al. 2009). It can be demonstrated that climate change nappe stacking. A more detailed description of the has led to significant changes in precipitation and the geological setting is given in Schäffer et al. (2018). runoff behavior of rivers during recent decades The Tuxbachquelle (TQ) is situated within the 4-km- (Brunetti et al. 2006; Saidi et al. 2018). In addition, long and up to 60-m-deep gorge of the Tuxbach (Tux small catchment areas react immediately to weather Creek) next to Finkenberg (Figure 1). extremes, such as the expected increase in heavy rainfall The Tuxbachquelle originates in the Jurassic events or longer dry periods caused by climate change Hochstegen Formation. The structural strike is about (Rajczak, Pall, and Schär 2013). It is therefore to be 60° ENE parallel to the valley and dips approximately expected that springs at high elevations will be subject 70° NNW. From base to top, the Hochstegen Formation to larger discharge fluctuations and will dry out more contains thin layers of quartzite, phyllite, and brownish frequently in the future. Climate models predict a time marble, followed by sequences of grayish-blue banded shift of the precipitation maxima from summer to calcitic and dolomitic marbles. Within the footwall of winter as well as that precipitation will more often be the Hochstegen Formation, the topographically higher in the form of rain instead of snowfall (Gobiet et al. Ahorn Gneiss is exposed (Figure 1). It consists of ortho- 2014). The resulting change in runoff characteristics gneisses, which are primarily augen gneiss. The contact will be superposed by earlier snowmelt and a decrease between both units is described as autochthonous, par- in snow cover, especially below 2,000 m (Kobierska autochthonous, or allochthonous (Frisch 1968, 1980; et al. 2013; Gobiet et al. 2014). Because the demand Thiele 1976). Low mineralized, lime-unsaturated, and for electricity in winter is higher than that in summer, cold waters from the Ahorn Gneiss infiltrate the this effect is advantageous for hydropower production Hochstegen Formation, having a high karstification (Wagner et al. 2017). On the other hand, this is dis- potential (Sass, Heldmann, and Schäffer 2016). advantageous for the water supply, because in Austrian The Tuxertal is rich in caves like other regions of rural and tourist regions water consumption is Austria built by calcareous rocks (Christian and Spötl increased by 40 to 120 percent during the summer 2010; Spötl, Plan, and Christian 2016). Almost forty period (BLFUW 2012). caves are known in the middle and upper parts of the The water supply in rural Austria is largely in private valley, and the ongoing glacier retreat has allowed new hands. Tributary valleys of the Zillertal are character- discoveries in recent years (Spötl 2009). There are two ized by isolated single spring or single well water sup- recently gauged and officially catalogued caves within plies. Typically, they have small catchment areas or the Tuxbach gorge. Goldbründl cave, located 35 m hydraulic connections to fissures, fractures, and faults. above the Tuxbach level, is at least 14 m long and To provide a reliable water supply, it is necessary to tap 8 m deep and shows a very variable water level at its perennial springs with a sufficient long-term discharge lower end of at least 20 m (Spötl and Schiffmann 2014). rate. It is suspected that many small catchment areas The mouth of the Goldbründl into the Tuxbach is will not fulfill this requirement due to ongoing climatic located close to TQ-12 (Figure 2). Grabungshöhle is change. Although the Tuxbachquelle has been identi- situated about 50 m further east, with a length of at fied by water authorities as important for future water least 31 m and a depth of 12 m (Spötl and Schiffmann supplies, this spring has never been thoroughly inves- 2014). In the lowest part of this cave, the noise of the tigated due to its inaccessibility. The exact number of flowing water is audible at times. Recent silt and clay outlets, discharge rates, and the catchment area were deposits within the cave also indicate ongoing hydro- largely unknown. One tracer test was carried out at logical activity. both low and high runoff. The results are not only relevant to the water supply but are also interesting Preliminary investigations for a tunnel currently under construction (Fliegl 2017), further geothermal exploration (Sass, Several inspections of the Tuxbach gorge were carried Heldmann, and Lehr 2016; Sass, Heldmann, and out within several years, mainly during winter months Schäffer 2016), and nature conservation, because the due to the lower runoff and better accessibility. In the area is located in the recently expanded area of the section between the Grinbergbach (Grinberg Creek) High Alps Nature Park Zillertaler Alps. inflow and the confluence into the Zemmbach (Figure 1), only two springs have been observed. The Tuxbachquelle consists of several outlets over Study area alengthof80monthesouthernbankoftheTuxbach The study area is located on the northwestern edge of (Figure 2), numbered upstream from TQ-0 to TQ-12. All the Tauern Window, including several faults caused by outlets are located at the river level, with the exception of 72 R. SCHÄFFER ET AL.

Figure 1. Simplified geological map of the project area, modified after Schäffer et al. (2018) and Kogler (2018). Relief shading was taken from the Tyrolean Geographic Information System (2019). The continuous red line indicates the catchment area of the sink; dashed red lines mark possible extensions of the catchment relating to the Tuxbachquelle.

TQ-6, which is located 3 m above the Tuxbach. Most of 1,471 m (Figure 2). It likely was not recognized outlets of the Tuxbachquelle are completely flooded during earlier for two reasons. First, the Grinbergbach only periods of high water and are hardly recognizable. Even at infiltrates completely at relatively low runoff rates. low water levels, the discharge of some outlets can only be Secondly, quaternary deposits are filling this part of estimated due to the short path into the Tuxbach and the thehillside(Figure 1). There are various springs, fea- low flow gradient. It became evident that TQ-1 is perennial. turing discharge rates of several liters per second each, All other outlets are intermittent. The total discharge of the emerging from unconsolidated rocks at a distance of Tuxbachquelle varies from 70 to ca. 500 L/s. Goldbründl is 200 to 450 m below the sink (Figure 2). Thus, not only intermittent and delivers up to ca. 500 L/s. karstification but also expected high permeabilities of The Grinbergbach is the only perennial stream that the quaternary deposits could explain the flow path of drains the southern slope of the Tuxertal southwest of the Grinbergbach. However, comparisons of water Finkenberg (Figure 1). In comparison to the Ahorn temperature, electrical conductivity, and hydrochemi- Gneiss, the density of water bodies is significantly cal composition showed significant differences from lower in the Hochstegen Formation. Thus, it can be the Grinbergbach above the sink. The western springs assumed that a considerable part of the drainage takes are conceivably fed by the Zirbental, which in karst place underground. morphology is defined as a dry valley. The catchment A sink was identified in the riverbed of the area of the eastern spring is probably the Gamsberg Grinbergbach at 711 835 E, 5224 322 N at an altitude (Figure 2). ARCTIC, ANTARCTIC, AND ALPINE RESEARCH 73

Figure 2. Position plan of the measuring points for both tracer tests: light blue circles indicate springs; dark blue circles creeks. The map background was taken from the Tyrolean Geographic Information System (2019). Overview of the first and maximal uranine transit in the different measuring points during the tracer tests at low (QLOW) and high (QHIGH) runoff.

Methods significantly shorter intervals, often several times an hour. During the phase of indirect monitoring, only activated Tracer test schedule carbon bags and an autosampler were used. Due to the Two tracer tests were carried out, one at low runoff and much higher dilution, for the test at high runoff a tenfold one at high runoff. The experiments consisted of three higher amount of dye was used. phases (Table 1). In the first phase until the input of uranine, the measuring points were set up and natural Monitoring network backgrounds of relevant parameters, including extinction, water temperature, pH, electrical conductivity, and tur- The monitoring network included three stations within the bidity, were recorded. During the direct monitoring Grinbergbach, the Grinbergbachquelle (GBQ), all known phase, all measuring points were checked once to several springs within the Tuxbach gorge, and eight springs south times a day. Important measuring points were sampled at of Finkenberg (Figure 2, Table 2).Inthetracertestatlow

Table 1. Schedule for both tracer tests. Preparation Uranine intake Direct monitoring Indirect monitoring Test at low runoff in 2016 4 to 8 September 8 September, 10:30 a.m., 160 g 8 to 14 September 14 September to 11 October Test at high runoff in 2017 7 to 9 June 9 June, 9:35 a.m., 1.6 kg 9 to 13 June 14 to 29 June 74 R. SCHÄFFER ET AL.

Table 2. List of measuring points. was carried out with two portable fluorometers by Turner Altitude Designs (model Aquafluor) at an extinction rate of Measuring point Abbreviation Position (UTM 32T) (m) 515 nm. Multipoint calibration was performed on the Brunnhausquelle BHQ 712653; 5225049 1,170 μ Dornauquelle 1 DQ-1 713642; 5224986 1,131 devices at a concentration range of 0.1 to 200 g/L. Dornauquelle 2 DQ-2 713566; 5225017 1,126 Water samples were taken for immediate analysis in plas- Grünbergquelle GBQ 711849; 5224621 1,380 Grinbergbach—Upper GB-U 711859; 5224132 1,553 tic cuvettes or were filled unfiltered into brown glass section bottles and kept protected from light until measurements Grinbergbach—Middle GB-M 711850; 5224245 1,502 section were performed. Turbid samples were stored until the Grinbergbach—Lower GB-L 711931; 5224888 1,273 suspended matter was deposited. Extinction was cor- section Goldbründl—Confluence GO-C 713070; 5225538 897 rected using formulas from Cao et al. (2017) for pH and Goldbründl—Spring GO-S 713079; 5225494 916 from Leibundgut, Maloszewski, and Külls (2009)for Gamshüttenwegquelle 1 GQ-1 713217; 5225159 1,082 Gamshüttenwegquelle 2 GQ-2 713295; 5225092 1,101 water temperature. Consideration of uranine decomposi- Gamshüttenwegquelle 3 GQ-3 713227; 5225107 1,107 tion due to photolysis (Käß 2004) was not necessary, Lampnerquelle 1 LQ-1 713141; 5225259 1,055 Lampnerquelle 2 LQ-2 713170; 5225282 1,039 because the superficial flow path was quite short. Quelle in der Seiche QDS 713049; 5225431 990 In the experiment during high runoff, three auto- Tuxbach—Gorge TB-G 713066; 5225542 896 Tuxbach—Innerberg TB-I 711920; 5225522 949 samplers from Maxx (model P6 L) were placed in GB- Tuxbachquelle TQ-0 to TQ- 713199; 5225543 894–901 M, TQ-1, and TQ-11. The autosamplers were mainly 12 713108; 5225560 used to collect continuously water samples during the night, which were analyzed the following morning. In addition, the autosamplers were able to take samples runoff, TB-I served as a background measuring point and from GB-M, TQ-1, and TQ-11 for a few days during GB-U served as a background measuring point at high the period of indirect monitoring (Table 1). runoff in the tracer test. It was possible to sample the Activated carbon bags from Provital were applied for previously inaccessible GQ-1 for the tracer test at high the qualitative detection of uranine. Each sachet con- runoff. GO-S was installed due to the high discharge of tained 2.8 g activated carbon with a grain size of 0.5 to the Goldbründl. The uranine intake on the Grinbergbach 1.0 mm. This brand had performed best in our own was at 711859 E, 5224173 N at an altitude of 1,534 m. laboratory tests. The use of activated carbon is based on a method developed in the Alps by Bauer (1967, 1972) with our own modifications. The activated carbon bags Measurements were exposed to 110°C in a drying oven for 24 hours Position and weather station before use. Two activated carbon sachets were simulta- Coordinates and altitudes of the measuring points were neously emplaced for each measuring point. One bag was measured with GPS devices and checked with the changed daily during the preparation and direct monitor- Tyrolean Geographic Information System 3.0 (Tyrolean ing periods (Table 1) and served for the detection of the Geographic Information System 2019). All coordinates exact day of possible uranine passage. The other bag was are given in WGS 1984, UTM zone 32T; all altitudes are exposed to the spring or creek water for several days to given in meters above the Adriatic Sea. a few weeks to detect very low concentrations of uranine A weather station was operated from 24 August 2016 and was only exchanged between the direct and indirect to 14 September 2016 and from 28 June 2017 to monitoring periods. Collected bags were washed as 30 October 2017 on the Gamshütte at 1,921 m quickly as possible, usually in the afternoon in our impro- (Figure 1). The weather station (Davies, model Vantage vised laboratory. First, they were dehydrated in a drying Pro2) records air temperature, air pressure, wind direc- oven at 60°C. Then the eluent, which was composed of tion, wind speed, precipitation, humidity, and solar 12 ml of 96 percent ethanol and 4 ml of 15 percent caustic radiation. potash per 5 g of activated carbon, was freshly prepared before use to prevent coloration. Elution was carried out Uranine for 30 minutes in a brown tube in a slowly spinning Various fluorescent dyes are widely used in karst hydrol- rotator to prevent mechanical comminution of the coal ogy (Goldscheider et al. 2008; Leibundgut, Maloszewski, as well as turbidity of the eluate. Organic material and Külls 2009). Uranine was used because it can be attached to the activated carbon grains causes detected easily and is sufficiently accurate in the field. a fluorescence background upon elution, which may Due to health concerns, the water management authority remarkably affect the detection of low uranine concentra- did not approve an additional use of rhodamine (cf. tions (Bauer 1972). This occurred especially with the Behrens et al. 2001). The quantitative detection of uranine samples from the Tuxbach. Conclusions of the eluent ARCTIC, ANTARCTIC, AND ALPINE RESEARCH 75 extinction on the effective uranine concentration were saturation were measured at the beginning and end of the only qualitatively possible, because the extinction depends tracer tests with devices from WTW (universal pocket on many factors, such as uranine concentration in the meter Multi 340i) and HACH (portable meter HQd). In water, exposure time, grain size, and amount of activated addition, multiprobe logger systems (Manta Sub2, Eureka carbon. The extinction values were corrected for the blank Water Probes) were used to survey TQ-1 and GO-A in value and the natural background concentration. Results more detail. Parameters were recorded hourly in TQ-1 and of the activated carbon bags were divided into four cate- three times a day in GO-A at 8-hour intervals. The turbidity gories: no evidence, questionable evidence with minor of the Tuxbach and the outlets of the Tuxbachquelle was concentrations, strong evidence, and certain evidence of quantified with a portable turbidimeter from HACH uranine (Table 3). (model 2100Q is).

Discharge and runoff Hydrochemical parameters Depending on the local conditions, direct or indirect mea- Water samples were collected at the beginning and end of surement methods (Coldewey and Göbel 2015) were used the tracer tests and filled into two bottles of 100 ml each. to determine discharge and runoff. At TQ-1, a hydrometric Samples for cation analysis were acidified with hydro- vane (Ott Hydromet, Germany) was used at an improvised chloric acid to approximately pH 2. The concentrations weir. At other Tuxbachquelle outlets, if possible, the out- of sodium (Na+), potassium (K+), magnesium (Mg2+), 2+ 2+ + flow was manually diverted, dug, or channeled with mate- calcium (Ca ), strontium (Sr ), ammonium (NH4 ), − − 3− rial found in situ like pebbles, sand, or moss in order to be nitrite (NO2 ), nitrate (NO3 ), phosphate (PO4 ), sulfate 2− − − − able to fill the discharge into measuring cups or plastic (SO4 ), fluorine (F ), chloride (Cl ), and bromide (Br ) bags. Where such an approach was not possible, the dis- were analyzed with an ion exchange chromatograph from charge was estimated. Spring water and river water were Metrohm (device 882 Compacts IC plus). − easily distinguishable by measurements of turbidity, tem- The concentration of bicarbonate (HCO3 ) was titrated perature, and electrical conductivity. on-site with a digital titrator from HACH (model 16900). In addition, two wildlife observation cameras were The titration sample was buffered with sulfuric acid to pH installed next to TQ-1 and GO-S following the high 4.3, indicated by the color change of Bromcresol green runoff rate experiment. Pictures taken at regular inter- methyl orange (C21H14Br4O5S, C14H15N3O3S). vals allowed quantitative estimations of the discharge rates and water turbidity. Results Physicochemical parameters Tracer test at low runoff rate (September and Water temperature and pH were defined at least once a day October 2016) at all measuring points in order to correct the measured extinction values. Temperature, pH, electrical conductivity In late summer, runoff from the Grinbergbach varied (at 25°C), redox potential (EH), oxygen content, and oxygen about 5 L/s and infiltrated completely into the sink. The

Table 3. Qualitative classification of the activated carbon bags of the tracer test at low runoff. Short-term activated carbon bags (days in September) Long-term activated carbon bags Measuring point 7–88–99–10 10–12 12–14 08/09–14/09 14/09–11/10 BHQ −− − − − DQ-1 −−−+ DQ-2 −−− GBQ − + −− ++ GB-U −−− GO-C −− − − − − GQ-1 −−−− GQ-2 −− − − − − GQ-3 −− − − − LQ-1 −− − − − LQ-2 −− − − − + QDS −− − − − − − TB-I −−−− TB-G −−−−−+ TQ-1 − + −− − − ++ TQ-2 −− − − − − + TQ-4 −− − − − − TQ-10 −− − − Note: − = no evidence; + = possible evidence of traces; ++ = strong evidence. Empty fields indicate no sample. 76 R. SCHÄFFER ET AL. creek bed below was dry from the sink to the before uranine input. These values were considered as Grinbergalm (Figure 2). In the initial test phase, TQ-1 natural backgrounds. Noticeable values were detected to TQ-5 and TQ-10 were running; all other outlets of in almost all monitored outlets of the Tuxbachquelle the Tuxbachquelle were dry. TQ-10 dried out on (TQ-2, TQ-4, and TQ-10) on 8 September (Figure 3), 10 September. The water temperatures and electrical peaking 4½ to 6½ hours after uranine input. A second conductivities of the Tuxbachquelle outlets were in an but lower maximum occurred between 9 and 11 hours identical range (Table 4) and differed significantly from after the input. In addition, two elevated values were Goldbründl (GO-C) and Tuxbach (TB-I). Turbidity found in DQ-1 on 9 September: 1.5 at 11:00 a.m. and was particularly appropriate to distinguish the clear 0.9 at 2:30 p.m. At all other measuring points no spring water (0.1 FNU to 4.3 FNU) from the turbid increased extinctions were observed. creek water (250 FNU to 410 FNU; Table 4), because Traces of uranine were detected in TQ-1 from 8 to the values differed by at least two orders of magnitude. 9 September and in GBQ from 10 to 12 September. The Goldbründl was almost dry on 14 September and Uranine was reliably detected in TQ-1 and GBQ within had a discharge rate lower than 0.1 L/s on 11 October. the second long-term exposure period, and possible TQ-3, TQ-4, and TQ-5 were dry on 11 October. uranine traces were found in DQ-1, LQ-2, TB-G, and Table A1 in the Appendix shows the properties of TQ-2. All other findings were negative. spring waters in comparison to the Grinbergbach. The blank extinction was 0.2. An extinction rate of Tracer test at high runoff rate (June 2017) up to 0.4 in springs and up to 2.0 in creeks was found This tracer test took place after several days of heavy rainfall causing about 30 L/s of runoff from the Table 4. Comparison of selected parameters of the measuring Grinbergbach. The sink was not able to contain the points within the Tuxbach gorge from 8 to 14 September 2016. entire runoff and approximately 5 L/s did overflow. Measuring κ at 25°C Turbidity point Q (L/s) T (°C) pH (µS/cm) (FNU) At the beginning, all known outlets of the TQ-1 190–275 6.1–6.5 7.62–8.29 133–152 0.1–2.1 Tuxbachquelle were running. TQ-1, TQ-4, TQ-9, TQ- TQ-2 19 6.1–6.4 7.93–8.34 134–153 2.0–2.4 TQ-3 0.2–2.3 6.1–6.9 7.46–8.29 132–152 1.5–3.0 10, TQ-11, and TQ-12 were chosen for regular mea- TQ-4 ca. 2 6.1–6.5 7.58–8.35 135–139 1.5–4.3 surements, because these outlets presented the largest TQ-5 ca. 100 6.1–6.2 8.20 143 2.1–3.8 TQ-10 <0.05 6.4–6.8 8.21 145–155 4.1 discharge and provided a comprehensive spatial repre- GO-C 0.3–1.9 8.2–10.0 7.98–8.38 169–220 0.7–1.2 sentation (Figure 2, Table 5). For comparison, TQ-0, – – – – – TB-G 3,000 3,500 10.5 13.2 8.34 8.39 304 338 250 410 TQ-3, TQ-5, and TQ-6 were measured sporadically.

Figure 3. Measured extinctions in the Tuxbach gorge during the first hours of the tracer test at low runoff. ARCTIC, ANTARCTIC, AND ALPINE RESEARCH 77

Table 5. Comparison of selected parameters of the measuring points within the Tuxbach gorge from 7 to 29 June 2017. Measuring point Q (L/s) T (°C) pH κ at 25°C (µS/cm) Turbidity (visual) TQ-0 0–0.25 5,2 8.25 126 Clear TQ-1 262–330 5.0–5.5 8.27–8.47 103–138 Clear to slightly muddy TQ-3 ca. 15 5.0 8.25 112 Clear to slightly muddy TQ-4 5.0–5.6 8.25–8.36 102–138 Clear to slightly muddy TQ-5 ca. 110–115 5.0 8.25 112 Clear TQ-6 ca. 0.25 5.0 8.29 111 Clear TQ-9 ca. 4–5 4.9–5.4 8.17–8.38 104–138 Clear TQ-10 ca. 25–30 4.9–5.2 8.16–8.38 104–138 Clear TQ-11 ca. 44–50 5.0–5.3 8.07–8.31 104–138 Clear TQ-12 ca. 3–10 4.9–5.3 8.14–8.33 104–138 Clear GO-S ca. 0.25–1,000 5.2–5.6 8.15–8.48 106–115 Clear GO-C 6.1–6.6 8.11–8.20 115–144 Clear TB-G 5,300–5,700 8.4–12.8 8.17–8.31 245–277 Heavily muddy

Most of the runoff had to be estimated visually because In GB-L, in the direct outflow of the sink (Figure 2), of the elevated discharge rates. TQ-2 could not be increased extinctions were noted a few hours after uranine investigated at all because this outlet was flooded by input (Figure 4). Maximum extinction occurred on 11 June, the Tuxbach. However, the activity was visible because 48½ hours after the input. On 29 June, at the end of the of the slighter turbidity of the Tuxbach. indirect monitoring period, increased extinctions were still There were significant changes in the discharge rates measurable in this section of the Grinbergbach. In single of all outlets of the Tuxbachquelle on direct monitoring measurements for comparison, significantly increased days (Table 1). On 10 June all outlets showed a much extinctions were detectable from 9 to 11 June in the small higher discharge rate than on the previous day, pre- creek east of GBQ but not in the GBQ itself. sumably as a result of intense precipitation during the In contrast, no noticeable elevated extinction was night. Floods repeatedly caused equipment losses dur- found in any other spring, including the outlets of the ing the night from 10 to 11 June and from 11 to 12 June Tuxbachquelle, until 13 June. However, using the auto- below Goldbründl. During 13 June Goldbründl swelled samplers positioned at TQ-1 and TQ-11, uranine pas- within several hours from a runlet to a creek dischar- sage was detected from 13 to 15 June (Figure 4). ging in a range of 0.75 to 1 m3/s. Unfortunately, a longer sampling was not possible due

Figure 4. Measured extinctions during the tracer test at high runoff at selected measurement points in June 2017. 78 R. SCHÄFFER ET AL. to the exhausted batteries. Thus, it is uncertain whether DQ-1, GQ-1, GQ-2, LQ-2, and QDS may indicate the uranine peak (measured extinctions of 1.59 and traces of uranine. 2.10, respectively) took place on 15 June or several A wet landslide, triggered by a half-hour summer days later. This evidence of uranine was not an artifact thunderstorm with hail, occurred on the evening of related to the autosamplers. Increased extensions 24 June. According to local witnesses, it was the fiercest amounting to up to 0.55 to 1.03 in TQ-1, TQ-11, and mudflow during the last 75 years in the Grinberg area. GO-S were also detected directly on 28 and 29 June The mudflow initiated from a steep, snow-covered sec- during the final sample collection. tion of the northeastern flank of the Grinbergspitze at Analysis of the activated carbon bags supported the about 2,240 m and descended following the flow path of above results (Table 6). An activated carbon bag placed the Grinbergbach to the Tuxbach. The creek bed of the for comparison between the input position and sink (at Grinbergbach was completely reworked and boulders of GB-S) achieved the largest extinction, followed by the up to a few meters were transported. In doing so, the bags from GB-L. Because the Grinbergbach was over- autosampler positioned at GB-L was destroyed and lost. flowing the sink, this finding is not surprising. It is rather interesting that the uranine was still detectable for at least four days after its input in the upper part of Additional investigations (July and August 2017) the Grinbergbach: the last measurement on 14 June resulted in a measured extinction of 34.9 (Figure 4). In order to examine the impact of the mudflow on the Traces of uranine reached the Tuxbach gorge (measur- sink hole, further investigations were performed in July ing point TB-G; Figure 2) via the superficial flow path and August at TQ-1 (Figure 5) and GO-A (Figure 6). It on the same day (Table 6). Larger amounts were found became evident that the Tuxbachquelle responds within in the following days. Traces of uranine were also a few hours to precipitation events: the discharge detectable in GBQ during the same period. Uranine increases significantly, electrical conductivity decreases, reached Goldbründl (GO-C) for the first time on and temperature increases slightly. These effects coin- 11 June and several outlets of the Tuxbachquelle on cide temporarily with maximum precipitation and 12 June and was then detected repeatedly in trace con- a temporary turbidity. Water temperature rises slightly centrations. In the long-term bags, high extinctions and electrical conductivity rises significantly during were measured from 13 to 28 June, providing reliable longer dry periods. A typical increase is within the proof of uranine. In addition, single long-term bags in range of 45 to 80 µS/cm.

Table 6. Qualitative classification of the activated carbon bags of the tracer test at high runoff. Short-term activated carbon bags (days in June) Long-term activated carbon bags (days in June) Measuring point 8–99–10 10–11 11–12 12–13 8–13 13–28 BHQ −−−−− − DQ-1 −−−−− + DQ-2 −−−−− − GBQ − ++++ + ++ GB-U − () −− () GB-M +++ GB-L +++ +++ +++ +++ +++ () GO-C −− + () + + +++ GQ-1 − + GQ-2 −−−−− − + GQ-3 −−−−− − − LQ-1 −−−−− − − LQ-2 −−−−− − + QDS −−−−− − + TB-G − + ++ + ++ ++ ++ TQ-1 −− − ++ + + TQ-4 −−−−− + +++ TQ-9 −− − − ++ ++ TQ-10 −− − + + + +++ TQ-11 −− − + + + +++ TQ-12 −− − + + + +++ Note: − = no evidence; + = possible evidence of traces; ++ = strong evidence; +++ = certain evidence of uranine; () = damage or loss of samples due to floodwater or mudflow. Empty fields indicate no sample. ARCTIC, ANTARCTIC, AND ALPINE RESEARCH 79

Goldbründl shows a pattern of daily temperature GB-L, and 29 percent took the underground flow path oscillation, typically within the range of 0.8°C to 1.2° and reached the Tuxbachquelle or Goldbründl. Despite C. Maxima take place shortly after midday and minima the uncertainties regarding the recovery rate, it can be occur around midnight. Heavy rainfall events interrupt assumed that the measuring network is complete and this pattern (Figure 6). As in the Tuxbachquelle, tem- that uranine did not leak at unknown locations. perature and electrical conductivity drop within a few hours after the beginning of precipitation events. In dry periods, the original conductivity recovers within a few Residence time and average flow velocity hours, whereas the water temperature rises for days. In Including the vertical height, the direct flow distance summary, Goldbründl is much more sensitive to between the sink and Tuxbachquelle or Goldbründl is weather than Tuxbachquelle. 1,920 m. The distance between the sink and measuring point GB-L is 570 m. The flow time between input Discussion location and sink (distance 150 m) was neglected, because the flow time was only a few minutes. Uranine recovery For the tracer test at low runoff, the uranine peak con- The recovery rate for the test during high runoff was centration reached different outlets of the Tuxbachquelle 106 percent of the amount of uranine used. This calcu- after4½to6½hours(Figure 2). These times are similar to lation includes an extinction correction for pH, water those of the observed response of the Tuxbachquelle and temperature, and natural background. Because dis- Goldbründl to heavy precipitation of a few hours (Figures 5 charge or runoff was often estimated, this inaccuracy and 6). This results in an average flow velocity of 0.08 to might be the reason for the apparently too high recov- 0.12 m/s or 300 to 425 m/h. In the tracer test at low runoff, ery rate. Seventy-seven percent of the uranine passed the maximum uranine concentration arrived much later in the Grinbergbach below the sink at measuring point the Tuxbachquelle; that is, 140½ hours after the input. This

Figure 5. Water temperature, electrical conductivity, and quantitative estimated turbidity at the Tuxbachquelle (outlet TQ-1) in comparison to precipitation at Gamshütte. Important precipitation events are marked with a gray background. 80 R. SCHÄFFER ET AL.

Figure 6. Water temperature, electrical conductivity, and estimated discharge based on photos at Goldbründl (measuring point GO- A) in comparison to precipitation at Gamshütte. Important precipitation events are marked with a gray background.

− resulted in an average flow velocity of 4 ∙ 10 3 m/s or 14 m/ Karstification of the Hochstegen Formation h. Interestingly, the average flow velocity between the sink − Assuming the karst system to be completely water satu- and GB-L was very similar, amounting to 3 ∙ 10 3 m/s or rated at the moment of uranine infiltration and the run- 12 m/h. The maximum uranine concentration occurred in out to take place exclusively at the Tuxbachquelle and the GB-L 48½ hours after the input (Figure 2). Goldbründl, a void volume of 190,000 to 330,000 m3 was The residence time and average flow velocity estimated for the Hochstegen Formation between the sink between the sink and Tuxbachquelle or Goldbründl and Tuxbach gorge, depending on supposed discharge were highly variable; that is, they were 25 times longer rates. Grabungshöhle and Goldbründl Cave are therefore at high runoff than at low runoff. The high runoff, manifestations of a much larger karst system. caused by the intense rainfalls at the beginning of June 2017, might have resulted in saturation and temporary storage of infiltrated water within the karst Catchment area system. The water was retained for days at narrow passages, resulting in a significant delay of the uranine The Austrian Hydrographic Service runs three precipi- transit. The flow velocities in the karst at high runoff tation measurement stations in the vicinity of − were connatural to a flow velocity of 1.7 ∙ 10 4 m/s Finkenberg (Lanersbach, #102 640; Geschößwand, obtained in karstified and saturated parts of the #103 192; and Ginzling, #102 632). From 2010 to Hochstegen Formation below Finkenberg at a depth 2014, the mean precipitation was 1,290 mm (AHS of 340 m (Lehr and Sass 2014). 2019). According to BLFUW (2013), the potential eva- Most of the uranine did not reach the lower section poration on the north side of the Alpine main ridge is of the Grinbergbach (GB-L) via the superficial flow in the range of 294 to 469 mm at an altitude of 1,350 to path but underground through the quaternary deposits. 1,940 m. Based on data for one year, the storage change This estimation coincides with the observation during is negligible, so it was assumed that the mean water high runoff in June 2017. About 85 percent of the supply is 0.91 m/a. Thus, a 2.4 km2 catchment area is Grinbergbach discharge infiltrated the sink and 15 per- required for a discharge of 70 L/s and an area of about cent of the volume followed the creek bed. 7.0 km2 for 200 L/s. ARCTIC, ANTARCTIC, AND ALPINE RESEARCH 81

The geographic catchment area of the sink, assessed up to 6.4 km2. This extension could explain the over 1.9 km2 (Figure 1), is apparently too small to observed discharge rates and temperatures at the solely feed the discharge of the Tuxbachquelle, despite Tuxbachquelle. Hydrological studies in other Alpine taking into account contributions of melting dead ice regions showed that rock glaciers can impact the andacirqueglaciertotherunoffoftheGrinbergbach. water quality extensively and can yield a base runoff The catchment area of the Tuxbachquelle possibly of 70 to 100 L/s during summer months (Nickus et al. extends to Zirbental and Brunnhauswald. This would 2015; Thies et al. 2013, 2017; Engel et al. 2019). increase the catchment area to 4.2 km2,althoughpre- vious field observations did not find evidence of Conclusion a contribution of the Brunnhauswald area. An extension of the catchment area, exceeding the Tux Main All outlets of the Tuxbachquelle had identical hydro- Ridge in the southern or eastern direction (Figure 1), chemical and physicochemical properties and can can be dismissed for morphological, geological, and therefore be classified as a spring group. Uranine was hydrogeological reasons. The geometry of fabric ele- detected in several active outlets. Thus, a hydraulic ments or tectonic features does not fit to be considered connection between the Tuxbachquelle and the sink as hydraulically effective pathways crossing the Tux on the Grinbergalm is proven. The Tuxbachquelle is Main Ridge in this area (Behrmann and Frisch 1990; a karst spring with variable discharge in the range of Lammerer and Weger 1998). Nappe thrust faults, the about 70 to 200 L/s. During or after precipitation Olperer Shear Zone, and the foliation of the Ahorn events, discharge can increase up to 500 L/s. Only out- Gneiss are all roughly southwest to northeast. The let TQ-1 is perennial; all other outlets are gradually terrain drops steeply toward the Zemmtal on the activated with rising runoff rates. other side of the ridge. Drainage takes places mostly In the Goldbründl, uranine was detected both by overground toward the Zemmbach because the Ahorn direct measurements and by the activated carbon Gneiss can hardly absorb precipitation. At the bags, proving a hydraulic connection to the sink on Gamsberg, a glacially smoothed high elevated flat the Grinbergalm as well. The measuring point at the (Wirsig et al. 2016), a mountain splitting caused eleven spring (GO-S) is much more suitable for investigations mostly west–east aligned grooves up to 500 m long than the one at the confluence in the Tuxbach (GO-C). and up to 12 m deep, which also dewater to the Despite the short flow path, relevant parameters change Zemmbach. due to contact with the air and the inflow of a small In June 2017, the upper Grinbergbach (measuring intermittent stream. The Goldbründl is an intermittent point GB-U) had temperatures of 7.5°C to 10.1°C, karst spring. For most of the year, there is a rather low whereas the Tuxbachquelle had temperatures of 4.9°C (<0.1 L/s) or even no discharge. After heavy rainfall, the to 5.6°C. This relatively low temperature range gives discharge increases within a few hours and can appar- strong evidence that a significant amount of the dis- ently reach 500 L/s. Goldbründl is very similar to the charge originates from higher altitudes and/or rock Tuxbachquelle regarding hydrochemical and physico- glaciers (Krainer and Mostler 2002). Considering the chemical properties. Therefore, it can be considered as water balance and water temperature, it is likely that an elevated outlet of the Tuxbachquelle. the catchment area of the Tuxbachquelle extends in the Low uranine concentrations could also be detected strike of the Hochstegen Formation to the southwest in the Grünbergquelle by means of activated carbon (Figure 1). It drains rock glaciers within the Elskar and bags in both tracer tests. The Grünbergquelle is con- the Lange Wand Kar area and conceivably other cir- sidered a pocket spring, fed from the quaternary depos- ques further west (Kogler 2018). As the existence of its in the upper part of the Grinbergalm (Figure 1). The several caves demonstrates, the Hochstegen Formation filtrate of the sink crosses the catchment area, causing is karstified there (Spötl 2009). The significantly lower the spring to be a mixture of infiltrated Grinbergbach density of surface water compared to the Ahorn Gneiss water and vadose water. at the other side of the Tux Main Ridge supports this No significant uranine signal was detected at all finding. In a field of roughly 700 to 100 m at the lower other monitored springs southwest of Finkenberg. end of the Lange Wand Kar rock glacier, we found Therefore, there is no evidence of further hydraulic twelve sinks and six dolines (cf. Kogler 2018) that connections from the sink. Nevertheless, noticeable possibly feed the Tuxbachquelle. Both Elskar rock gla- extinctions were derived from single activated carbon ciers are hardly accessible and therefore only a few bags in DQ-1 and LQ-2 in 2016 and in GQ-1, GQ-2, sinks have been found so far. The catchment area of and QDS in 2017. It is assumed that naturally occurring the sink, Zirbental, Elskar, and Lange Wand Kar, adds organic material in the spring water, instead of the 82 R. SCHÄFFER ET AL. applied uranine, was responsible for the extinction, Funding because (1) these findings were not reproducible, (2 The publication fee was covered by the German Research neighboring springs were not affected, and (3) the Foundation (DFG) and the Open Access Publishing Fund extinctions were above the natural background values, of Technische Universität Darmstadt. though only slightly.

Outlook ORCID Rafael Schäffer http://orcid.org/0000-0002-9717-6496 Stevanović (2019) estimated how climate change, population growth, and other factors will impact karst aquifers suitable for water supply. On a global References perspective, only a minor part of annually renewable karstic groundwater is currently exploited, resulting in AHS (Austrian Hydrographic Service). Bundesministerium a large potential. Our study is a local example of how Nachhaltigkeit und Tourismus. Accessed May 10, 2019. a study could be carried out to investigate such unused http://ehyd.gv.at/#. water resources. The discharge of the Tuxbachquelle is Auer, I., R. Böhm, A. Jurkovic, W. Lipa, A. Orlik, R. Potzmann, W. Schöner, M. Ungersböck, C. Matulla, sufficient to supply Finkenberg. Surveyed hydroche- K. Briffa, et al. 2007. HISTALP - historical instrumental mical and physicochemical parameters fulfill the climatological surface time series of the Greater Alpine requirements of the Austrian Drinking Water Region. International Journal of Climatology 27:17–46. Regulation (RIS 2019). Before its use as drinking doi:10.1002/(ISSN)1097-0088. water, microbiological examinations and the defini- Bauer, F. 1967. Erfahrungen beim Uraninnachweis mit tion of a spring reserve, considering the findings pre- Aktivkohle. Steirische Beiträge zur Hydrogeologie 1966/ 67:169–78. sented here, are essential. It might be necessary to Bauer, F. 1972. Weitere Erfahrungen beim Uraninnachweis restrictthealpinepastureattheGrinbergalm.For mit Aktivkohle. Geologisches Jahrbuch C2:19–27. a better evaluation of the catchment area of the Behrens, H., U. Beims, H. Dieter, G. Dietze, T. Eikmann, Tuxbachquelle, further field observations and investi- T. Grummt, H. Hanisch, H. Henseling, W. Käß, gations are required. Firstly, the assumed hydraulic H. Kerndorff, et al. 2001. Toxicological and ecotoxicologi- cal assessment of water tracers. Hydrogeology Journal connection to the west should be verified by means 9:321–25. doi:10.1007/s100400100126. of tracer tests. Secondly, in the case of positive find- Behrmann, J. H., and W. Frisch. 1990. Sinistral ductile shear- ings, the influence of rock glaciers on water quality ing associated with metamorphic decompression in the should be examined in more detail. In order to reduce Tauern Window, Eastern Alps. Jahrbuch der Geologischen – the uncertainties of the calculations presented here, Bundesanstalt 100:135 46. the construction of weirs at the Grinbergbach BLFUW (Bundesministerium für Land- und Forstwirtschaft). 2012. Wasserverbrauch und Wasserbedarf – Auswertung and the outlets of the Tuxbachquelle is required for empirischer Daten zum Wasserverbrauch. Bundes- more accurate runoff determination. Due to the pro- ministerium für Land- und Forstwirtschaft, 35 p., Umwelt ven karstification of the Hochstegen Formation, karst und Wasserwirtschaft, Wien. doi:10.1094/PDIS-11-11-0999- cavities and considerable water invasion will impede PDN. the ongoing tunneling. BLFUW (Bundesministerium für Land- und Forstwirtschaft). 2013. Hydrographisches Jahrbuch von Österreich, 119. Band 2011. Wasserverbrauch und Wasserbedarf – Acknowledgments Auswertung empirischer Daten zum Wasserverbrauch, 967 p., Bundesministerium für Land- und Forstwirtschaft, Julian Formhals, Christopher Hesse, Meike Hintze, Hung Umwelt und Wasserwirtschaft, Wien. Pham, Dirk Scheuvens, Gaby Schubert, Rainer Seehaus, Brighenti, S., M. Tolotti, M. C. Bruno, M. Engel, G. Wharton, Franziska Stemke, and Bastian Welsch helped with tracer L. Cerasino, V. Mair, and W. Bertoldi. 2019. After the peak tests. Participants of the field exercise “Hauptgeländeübung II water: The increasing influence of rock glaciers on alpine – 2016” collected samples during the tracer test at low runoff. river systems. Hydrological Processes 33:2804 23. Data from the gauge Persal were provided by the doi:10.1002/hyp.v33.21. Hydrographical Service of Tyrol and the gauge’s operator, the Brunetti, M., G. Lentini, M. Maugeri, T. Nanni, I. Auer, Verbund Hydro Power Ltd. Comments from an anonymous R. Böhm, and W. Schöner. 2009. Climate variability and reviewer and the editor significantly improved the article. change in the Greater Alpine Region over the last two centuries based on multi-variable analysis. International Journal of Climatology 29:2197–225. doi:10.1002/joc.1857. Disclosure statement Brunetti, M., M. Maugeri, T. Nanni, I. Auer, R. Böhm, and W. Schöner. 2006. Precipitation variability and changes in No potential conflict of interest was reported by the authors. the greater Alpine region over the 1800–2003 period. ARCTIC, ANTARCTIC, AND ALPINE RESEARCH 83

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Appendix

Table A1. Chemical properties of Grinbergbach at low runoff compared to spring water at the beginning and end of the tracer test. Samples taken in September 2016. Measuring point GB-U GBQ GBQ BHQ BHQ QDS QDS Date 05/09 05/09 14/09 05/09 14/09 04/09 14/09 T (°C) 10.8 5.9 6.0 7.0 6.7 11.2 9.2 κ at 25°C (µS/cm) 76 51 52 114 115 246 252 pH 7.87 7.57 7.09 7.66 7.18 7.52 7.24 EH (mV) 304 348 335 337 314 299 333 O2 content (mg/L) 9 10 11 10 10 8 9 O2 saturation (%) 101 99 101 95 96 88 89 Q (L/s) ca. 5 1.32 0.50 1.53 1.20 0.54 0.25 Na+ (mg/L) 0.01 0.32 0.28 0.88 0.97 3.46 3.14 + NH4 (mg/L) <0.01 0.02 0.04 <0.01 <0.01 <0.01 <0.01 K+ (mg/L) 0.44 0.76 0.73 1.20 1.21 2.57 2.44 Mg2+ (mg/L) 2.05 0.88 0.85 2.30 2.32 4.31 4.32 Ca2+ (mg/L) 12.8 8.65 8.75 19.3 19.5 44.5 44.8 Sr2+ (mg/L) <0.1 <0.1 <0.1 0.18 0.15 0.19 0.22 F− (mg/L) 0.02 0.03 0.03 0.07 0.06 0.05 0.05 Cl− (mg/L) 0.50 0.72 0.12 0.75 0.72 6.74 6.53 − NO2 (mg/L) 0.01 <0.01 < 0.01 0.01 <0.01 <0.01 <0.01 Br− (mg/L) 0.09 0.08 0.06 0.13 0.11 0.37 0.21 − NO3 (mg/L) 0.98 1.89 1.78 1.69 3.57 7.81 7.52 3− PO4 (mg/L) 0.09 0.09 0.06 0.09 0.07 0.04 0.05 SO 2− (mg/L) 1.82 2.46 2.50 5.11 5.11 3.32 3.43 4 − HCO3 (mg/L) 46.4 28.1 28.1 65.9 65.9 149 142 TDS (mg/L) 65.2 44.0 43.3 97.6 99.7 222 214 Δ ion balance (%) −1.63 −5.16 −1.48 −1.31 −2.40 −1.42 3.32 Measuring point GQ-2 GQ-2 GQ-3 GQ-3 LQ-1 LQ-1 LQ-2 LQ-2 Date 06/09 14/09 06/09 14/09 07/09 14/09 07/09 14/09 T (°C) 7.1 7.5 7.8 8.0 8.3 9.1 9.4 10.5 κ at 25°C (µS/cm) 122 127 145 147 133 137 82 86 pH 8.01 7.41 7.87 7.53 7.86 7.53 7.82 7.24 EH (mV) 307 315 316 311 347 314 366 307 O2 content (mg/L) 10 10 8 9 11 10 10 10 O2 saturation (%) 92 93 80 85 100 99 101 100 Q (L/s) 0.63 0.60 0.06 0.05 0.22 0.05 0.16 0.07 Na+ (mg/L) 1.20 1.12 1.58 1.41 1.21 1.08 1.21 1.26 + NH4 (mg/L) <0.01 <0.01 0.01 0.02 <0.01 <0.01 0.02 <0.01 K+ (mg/L) 1.30 1.47 1.59 1.64 1.46 1.47 1.09 1.09 Mg2+ (mg/L) 2.05 2.50 4.31 4.45 2.82 2.77 2.10 2.25 Ca2+ (mg/L) 21.5 22.2 22.2 22.8 23.1 23.8 11.8 12.8 Sr2+ (mg/L) 0.22 0.21 0.30 0.29 0.13 <0.1 0.14 0.13 F− (mg/L) 0.07 0.07 0.09 0.08 0.09 0.09 0.08 0.08 Cl− (mg/L) 0.49 0.62 0.49 0.40 0.40 0.54 0.40 1.02 − NO2 (mg/L) <0.01 <0.01 <0.01 <0.01 0.01 <0.01 <0.01 0.07 Br− (mg/L) 0.11 0.11 0.12 0.17 <0.01 0.13 0.07 0.10 − NO3 (mg/L) 2.02 1.90 1.01 1.10 <0.01 1.03 2.02 2.21 3− PO4 (mg/L) 0.06 0.05 0.07 0.05 0.04 0.05 0.05 0.05 SO 2− (mg/L) 5.40 5.74 8.47 8.72 5.24 5.37 5.21 5.75 4 − HCO3 (mg/L) 72.0 68.3 81.8 83.0 83.0 79.3 43.9 43.9 TDS (mg/L) 106 104 122 124 117 116 68.2 142 Δ ion balance (%) −1.00 8.06 1.45 2.43 −0.61 3.26 −3.51 3.32 Measuring point DQ-1 DQ-1 DQ-2 DQ-2 TQ-1 TQ-1 GO-C Date 06/09 14/09 06/09 14/09 04/09 14/09 14/09 T (°C) 7.1 8.3 6.7 7.4 5.7 6.1 9.4 κ at 25°C (µS/cm) 128 125 124 141 137 152 220 pH 7.71 7.96 7.74 7.74 8.06 8.31 8.43 EH (mV) 278 392 287 311 272 354 346 O2 content (mg/L) 10 10 10 8 9 10 10 O2 saturation (%) 100 99 90 87 119 85 98 Q (L/s) 1.90 1.21 0.47 0.64 5.7 6.1 <0.1 Na+ (mg/L) 1.12 1.07 1.03 1.15 0.78 0.95 2.15 + NH4 (mg/L) <0.01 <0.01 <0.01 0.04 0.02 <0.01 0.03 K+ (mg/L) 1.21 1.21 1.22 1.27 0.81 0.78 1.56 Mg2+ (mg/L) 1.59 1.71 1.90 1.92 3.19 3.43 4.19 Ca2+ (mg/L) 23.3 24.3 22.0 22.4 21.7 23.6 34.6 Sr2+ (mg/L) 0.21 0.18 0.07 0.20 0.08 0.11 0.11 F− (mg/L) 0.06 0.06 0.06 0.07 0.06 0.08 0.07 Cl− (mg/L) 0.39 0.68 0.81 0.62 0.75 1.15 3.95 − NO2 (mg/L) <0.01 0.01 <0.01 <0.01 0.04 <0.01 0.01 (Continued) 86 R. SCHÄFFER ET AL.

Table A1. (Continued). Measuring point GB-U GBQ GBQ BHQ BHQ QDS QDS Br− (mg/L) 0.12 0.14 0.12 0.11 0.12 0.13 0.16 − NO3 (mg/L) 3.02 1.92 1.87 1.84 1.46 1.34 4.08 3− PO4 (mg/L) 0.08 0.06 0.08 0.05 0.09 0.05 0.08 SO 2− (mg/L) 4.17 4.26 5.14 5.12 6.75 8.93 6.59 4 − HCO3 (mg/L) 73.2 78.1 75.7 67.1 73.2 73.2 115 TDS (mg/L) 108 110 114 102 109 114 172 Δ ion balance (%) 1.80 −5.57 0.68 8.01 0.91 5.34 0.32 Note: TDS = Total dissolved solids.